The present invention relates to a stretched, laminated film. More particularly, the present invention relates to a stretched, laminated film suitable as a wrapping film which is excellent in cuttability, transparency, heat-resistance, adherence, gas-barrier properties, anti-heat-shrinkage, and food safety.
As conventionally known packaging film (wrapping film) used for the purpose of packaging articles, for example, foodstuffs, etc., a film composed of polyvinylidene chloride, polyethylene or polyvinyl chloride as the main constituent can be exemplified. These wrapping films when used to package articles are often charged into an electronic oven to be heated, so that they must not only have good adherence but also be prevented from heat-shrinkage, melting, color change and the like when heated to a high temperature, in other words, to have a excellent heat resistance.
However, a polyvinylidene chloride film is disadvantageous in that the heat-shrinkage is large. A polyethylene film has a defect in that the film melts when it comes into contact with a hot oily substance such as hot meat and fried food. A polyvinyl chloride film whitens when it contacts boiling water.
As resins for a packaging film having heat-resistance, polyesters such as a polyethylene terephthalate (hereinunder referred to as "PET") are known. PET has both excellent heat-resistance and excellent mechanical strength, but it is difficult to impart adherence to PET. It is, therefore, difficult to use PET as a wrapping film in the form of a single-layer film. A wrapping film is required to have excellent cuttability. A wrapping film is generally sold and used in a case such as paper box from which the film is drawn out to the required length and cut off by bringing the film into contact with a cutting blade or "a cutting edge" which is attached to the case. As the "cutting edge" used for cutting off the film, a simple blade produced merely by blanking an iron plate of about 0.2 mm in thickness into the shape of a saw is generally used. The case holding the "cutting edge" is generally a paper box made of coated board having a strength of about 350 to 700 g/m.sup.2, so that the rigidity thereof is very low.
This type of film may be easy to cut by such a simple cutting mechanism as desired by the user. However actually, not only the case or the "cutting edge" is sometimes deformed but also the film is sometimes deformed or cut at a position other than perpendicular to the "cutting edge" more specifically, at the time of cutting, when a rift occurs on a conventional polyvinylidene film, the film has a tendency of being cut obliquely along the rift instead of along the "cutting edge". A conventional polyethylene film requires a considerable pulling force at the time of cutting, so that the case is sometimes bent and the film is sometimes deformed. Furthermore, a wrapping film which does not generate chlorine or the like during use or when burned, has recently been demanded for environmental reasons.
A packaging film comprising an inner layer and an outer layer composed of polypropylene composition, and an intermediate layer composed of an aliphatic polyamides was proposed as a wrapping film which generates no chlorine (Japanese Patent Application Laid-Open (KOKAI) Nos. 2-1605, 3-13550, 3-15547, and 3-283346).
In spite of these films, a laminated film composed of a chlorine-free resin polymer, and which has improved heat-resistance, adherence, gas-barrier property and easy cutting property is required.
It has been found that by stretching a laminate comprising a polyester such as a PET resin as an intermediate layer and a polypropylene composition as an outer layer and an inner layer composed of 100 parts by weight of polypropylene, 2 to 30 parts by weight of polybutene and/or polyisobutylene and 0.2 to 5 parts by weight of a polyglycerin fatty acid ester, the resultant stretched, laminated film has excellent cuttability, transparency, heat-resistance, adherence, gas-barrier property, anti-heat shrinkability and food safety, especially excellent heat-resistance and cuttability without impairing the intrinsic properties (heat-resistance and mechanical strength) of the polyester resin, and further is free of chlorine. The present invention has been achieved on the basis of this finding.